Im currently doing the MPI. I'd say that it has helped a lot with my speech but you have to put the work in to see results. Me personally, I haven't recently been putting in as much time as I should but definitely has helped a lot. I could honestly say that I don't know the last time I stuttered on a phone call or while ordering food, but some situations still catch me out such as on a call if someone is around or around friends because i find it hard using the technique as much.